Abstract Self-pillared pentasil MFI (∼1 nm diffusion length) exhibited low ethene selectivity (1.1%) at <100% conversion for the catalytic reaction of dimethyl ether (DME) at 723 K and ∼60 kPa DME pressure suggesting that the aromatics-based catalytic cycle is intrinsically suppressed in the pores of MFI under these reaction conditions. Co-feeding toluene or p-xylene with DME increased the number of chain carriers of the aromatics-based cycle, thereby enhancing its propagation and resulting in a 2-3-fold increase in ethene selectivity. Co-feeding propene or 1-hexene, however, did not have an effect on the product distribution, suggesting that the olefins-based hydrocarbon pool is saturated in the pores of MFI. At high temperature (723 K) and low DME space velocity (≤2.5 mol C [mol Al-s]-1), conditions resulting in complete DME/methanol conversion, the catalyst bed comprises two stages: The first stage performs methanol-to-hydrocarbons chemistry in the presence of DME/methanol; the second stage begins after 100% DME conversion is achieved and is characterized by the absence of DME/methanol. The aromatics-based methylation/cracking cycle is absent in the second stage as methylbenzenes cannot dealkylate in the absence of DME/methanol, and the dominant pathway to ethene formation under these reaction conditions is olefin inter-conversion.
Bibliographical noteFunding Information:
The authors acknowledge financial support from The Dow Chemical Company and the National Science Foundation (CBET 1055846). The authors also acknowledge Ms. Dandan Xu, University of Minnesota, for the synthesis of SPP MFI zeolite sample and Prof. Dongxia Liu, University of Maryland, for the synthesis of 3DOm-i MFI zeolite sample. The authors also acknowledge Mr. Kyle Weideman, University of Minnesota, for help with the experimental setup.
© 2015 Elsevier Inc.
- Aromatics-based catalytic cycle
- Diffusion free
- Ethene selectivity
- High conversion
- Low space velocity
- Olefins-based catalytic cycle